1. Field of the Invention
The present invention relates to an inkjet recording apparatus which is capable of ejecting particulate matter such as pigment matter and toner matter by making use of an electric field, and more particularly to an improved arrangement of the inkjet recording apparatus.
2. Description of the Related Art
There has recently been a growing interest in non-impact recording methods, because noise while recording is extremely small to such a degree that it can be neglected. Particularly, inkjet recording methods are extremely effective in that they are structurally simple and that they can perform high-speed recording directly onto ordinary medium. As one of the inkjet recording methods, there is an electrostatic inkjet recording method.
The electrostatic inkjet recording apparatus generally has an electrostatic inkjet head and a counter electrode which is disposed behind the recording medium to form an electric field. The electrostatic inkjet head has an ink chamber which temporarily stores ink containing toner particles and a plurality of ejection electrodes formed near the end of the ink chamber and directed toward the counter electrode. The ink near the front end of the ejection electrode forms a concave meniscus due to its surface tension, and consequently, the ink is supplied to the front end of the ejection electrode. If positive voltage relative to the counter electrode is supplied to a certain ejection electrode of the head, then the particulate matter in ink will be moved toward the front end of that ejection electrode by the electric field generated between the ejection electrode and the counter electrode. When the coulomb force due to the electric field between the ejection electrode and the counter electrode considerably exceeds the surface tension of the ink liquid, the particulate matter reaching the front end of the ejection electrode is jetted toward the counter electrode as an agglomeration of particulate matter having a small quantity of liquid, and consequently, the jetted agglomeration adheres to the surface of the recording medium. Thus, by applying pulses of positive voltage to a desired ejection electrode, agglomerations of particulate matter are jetted in sequence from the front end of the ejection electrode, and printing is performed. An inkjet head like this is disclosed, for example, in Japan Laid-Open Patent Publication No. 60-228162.
As another conventional example, there has been disclosed an electrostatic inkjet head having a gate electrode provided in front of an ink electrode in Japan Laid-Open Patent Publication No. 1-165452. The gate electrode has an opening or slit through which ink droplets are jetted. Since the distance between the gate electrode and the ink electrode is relatively short, ink ejection occurs when applying a lower driving voltage to the ink electrode.
However, when the inkjet head starts moving, vibrations from head movement cause the ink in the ink chamber to flow from the nozzle of the inkjet head to outside, which eventually forms an ink bridge between the nozzle and the opening of the gate electrode. There are cases where the opening of the gate electrode is blocked with the ink bridge and ink ejection becomes impossible, resulting in deteriorated printing quality. Even in the case of no ink bridge, the jetted ink is left in meniscus form in the opening of the gate electrode, which may also causes impossible ink ejection.